"In my mind I have gone all over the universe, which may make it less important for me to make piddling little trips... I did enjoy seeing Stonehenge. It looked exactly the way I thought it would look."
- Isaac Asimov

Early reference to the idea of radioactive fuel for space exploration.

And the fuel was almost gone - word had just come from the rocket rooms that the last chest of radio active protonite had been opened. In a few minutes the great liner would be at the questionable mercy of the Black Hawk.